A brushless DC (BLDC) motor is braked by generating a negative torque which slows the rotation of the motor. A periodic determination is performed to detect when the application of the braking torque should be discontinued. It may determine, for example, when a specified time interval has elapsed (a fixed braking time approach) or a sensed motor speed has achieved a desired threshold value (a speed sensing approach). One prior technique for braking uses the back electromotive force (EMF) voltage induced in a coil of the motor. This “passive braking” generates a negative torque by shorting a coil. Another braking technique that has been used in the past is “active braking”. Active braking provides an active excitation (by applying a drive current) to a motor coil to generate a braking torque. Active braking allows a much faster deceleration than passive braking.
Braking may be based on a fixed active braking time or employ speed sensing, as mentioned above. A drawback to the fixed time approach is that is does not adapt well to changing motor characteristics and can allow reverse motor spinning to occur. Speed sensing requires some type of feedback from the motor. In the case of active braking, the feedback may be based on the output of a magnetic field sensor, e.g., a Hall-effect sensor. Back EMF voltage has also been used for speed sensing, but only in three-coil motor applications. In that type of application, two active coils are used for active braking. A third, non-active coil is available for the back EMF speed sensing. The three-coil design thus enables continuous sensing in any of the three coils. The back EMF-based speed sensing uses a voltage measurement taken across the coil, since the peak amplitude of the back EMF voltage is proportional to the speed.